Refrigeration apparatus

ABSTRACT

Provided is a refrigeration apparatus which can reduce outlet pressure of a refrigerator even in overload conditions and which can improve refrigeration capacity by liquefying a refrigerant in an intermediate cooler. When outlet pressure of a refrigerator  2  is higher than critical pressure, a control apparatus  60  performs control to reduce the opening degree of a decompression electric valve  31  at the upstream side of an intermediate cooler  30 . Thereby, the refrigerant is liquefied by gas-liquid separation in the intermediate cooler  30 , so that the refrigerator outlet pressure is made less than the critical pressure, and the liquid refrigerant can be sent to a showcase  3 . As a result, the specific enthalpy of the refrigerant at the inlet side of main diaphragm means  41  of the showcase  3  can be reduced, and thereby, the cooling effect can be increased.

INCORPORATION BY REFERENCE

The present application claims priority under 35 U.S.C.§119 to Japanese Patent Application No. 2016-061616 filed on Mar. 25, 2016. The content of the application is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention is relates to a refrigeration apparatus, and more particularly to a refrigeration apparatus in which a refrigerant circuit is configured by a compressor, a gas cooler, an intermediate heat exchanger, and an evaporator, and in which the high pressure side is set to supercritical pressure.

Description of the Related Art

Conventionally, for example, in a large store, such as a supermarket, many refrigeration showcases and many cold storage showcases are installed. In the showcase, a refrigeration apparatus which operates a refrigerator is used in many cases.

Conventionally, in the refrigeration apparatus, for example, a technique is disclosed, in which the refrigeration apparatus includes: pressure regulation diaphragm means provided at the downstream side of a gas cooler and connected to a refrigerant circuit at the upstream side of main diaphragm means; and an intermediate cooler provided at the downstream side of the pressure regulation diaphragm means and connected to the refrigerant circuit at the upstream side of the main diaphragm means, and in which the opening degree of the pressure regulation diaphragm means is controlled by control means, and thereby, the pressure of refrigerant flowing into the main diaphragm means is adjusted to a predetermined specified value (see, for example, WO2014/068967).

SUMMARY OF THE INVENTION

However, in the technique described in WO2014/068967, there is a case where, even when the opening degree of auxiliary diaphragm means is maximum, the outlet pressure is not lowered to the specified pressure. Especially, there is a case where, for example, under an overload condition, such as in a midsummer day, the outlet pressure is higher than 7.3 MPa which is the critical pressure. In this case, there is a problem that, since the refrigerant cannot be liquefied in the intermediate cooler, the cooling effect cannot be improved by liquefaction, and hence, the cooling performance is degraded.

The present invention has been made in view of the above described problem, and an object of the present invention is to provide a refrigeration apparatus which can reduce outlet pressure of a refrigerator even in overload conditions and which can thereby improve the refrigeration capacity by liquefying refrigerant in an intermediate cooler.

In order to achieve the above-described object, according to the present invention, there is provided a refrigeration apparatus which includes: a refrigerator having a two-stage compression compressor, an intercooler, a gas cooler, a decompression electric valve, an intermediate cooler, and a gas return electric valve; and a showcase having main diaphragm means and a evaporator, the refrigeration apparatus being characterized by including a control apparatus which performs control to reduce the opening degree of the decompression electric valve at the upstream side of the intermediate cooler when the outlet pressure of the refrigerator is higher than the critical pressure.

Thereby, in the intermediate cooler, gas-liquid separation is performed and thereby the refrigerant is liquefied. As a result, the refrigerator outlet pressure is made less than the critical pressure, so that a liquid refrigerant can be sent to the showcase. Thereby, the specific enthalpy of the refrigerant at the inlet side of the main diaphragm means of the showcase can be reduced, and the cooling effect can be increased.

In the above-described configuration, when the difference between the high pressure at the discharge side of the compressor and the design pressure is less than 1 MPa, the control apparatus performs control to reduce the amount of rotation of the compressor.

In the above-described configuration, the control apparatus may also perform control such that, when the difference between the high pressure at the discharge side of the compressor and the design pressure is less than 1 MPa, the amount of rotation of the compressor is reduced, and such that, after the difference between the high pressure at the discharge side of the compressor and the design pressure is secured, the opening degree of the decompression electric valve is reduced.

According to the present invention, the refrigerator outlet pressure can be less than the critical pressure, and the liquid refrigerant can be sent to the showcase. Thereby, the specific enthalpy of the refrigerant at the inlet side of the main diaphragm means of the showcase can be reduced, and the cooling effect can be increased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a refrigeration cycle showing an embodiment of a refrigeration apparatus according to the present invention;

FIG. 2 is a block diagram showing a control apparatus in the present embodiment;

FIG. 3 is a flowchart showing control operation in the present embodiment; and

FIG. 4 is a p-h diagram in control of the present invention, and a p-h diagram in control of a conventional technique.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

A first invention provides a refrigeration apparatus which includes: a refrigerator having a two-stage compression compressor, an intercooler, a gas cooler, a decompression electric valve, an intermediate cooler, and a gas return electric valve; and a showcase having main diaphragm means and a evaporator, the refrigeration apparatus being characterized by including a control apparatus which performs control to reduce the opening degree of the decompression electric valve at the upstream side of the intermediate cooler when the outlet pressure at the refrigerator is higher than the critical pressure.

Thereby, in the intermediate cooler, the refrigerator outlet pressure can be made lower than the critical pressure, and hence, the refrigerant is separated into a gas refrigerant and a liquid refrigerant, so that the liquid refrigerant is sent to the showcase. Thereby, at the inlet side of the main diaphragm means of the showcase, the specific enthalpy of the refrigerant can be reduced, and the cooling effect can be increased.

A second invention provides a refrigeration apparatus characterized in that, when the difference between the high pressure at the discharge side of the compressor and the design pressure is less than 1 MPa, the control apparatus performs control to reduce the amount of rotation of the compressor.

According to this invention, the amount of rotation of the compressor is reduced, and thereby, the outlet pressure of the refrigerator can be reduced. In this case, when the amount of rotation of the compressor is reduced, the circulation amount of refrigerant is reduced. However, since the specific enthalpy of the refrigerant can also be reduced, the cooling effect can be increased, and the cooling capacity can be increased.

A third invention provides a refrigeration apparatus characterized in that the control apparatus performs control such that, when the difference between the high pressure at the discharge side of the compressor and the design pressure is less than 1 MPa, the amount of rotation of the compressor is reduced, and such that, after the difference between the high pressure at the discharge side of the compressor and the design pressure is secured, the opening degree of the decompression electric valve is reduced.

According to this invention, after the difference between the high pressure at the discharge side of the compressor and the design pressure is secured, the opening degree of the decompression electric valve is reduced, and thereby, the outlet pressure of the refrigerator can be reduced.

In the following, an embodiment according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a circuit diagram of a refrigeration cycle showing an embodiment of a refrigeration apparatus according to the present invention.

As shown in FIG. 1, a refrigeration apparatus 1 includes a refrigerator 2 cooling a refrigerant, and showcases 3 each cooled by the refrigerant sent from the refrigerator 2. The showcase 3 is installed in a facility, such as, for example, a convenience store and a supermarket, and cools displayed refrigerated and frozen products.

Further, in the present embodiment, the refrigeration apparatus 1 uses, as the refrigerant, carbon dioxide so that the high-pressure side refrigerant pressure (high pressure) is not less than the critical pressure (supercritical pressure) of the refrigerant. The carbon dioxide refrigerant is a natural refrigerant which is considered to be friendly to the global environment and to have properties, such as flammability and non-toxicity.

Further, the refrigerator 2 is provided with a compressor 10 which performs two-stage compression. A refrigeration heat exchanger 11 is connected to the compressor 10 via a refrigerant pipe 12. The refrigeration heat exchanger 11 is configured by a gas cooler 13, an intercooler 14, an oil cooler 15, and a blower fan 16.

In the compressor 10, a first compression mechanism is provided with a first suction port 20 and a first discharge port 21, and a second compression mechanism is provided with a second suction port 22 and a second discharge port 23.

The second discharge port 23 of the compressor 10 is connected to an oil separator 24 via the refrigerant pipe 12. The oil separator 24 is connected to the gas cooler 13 via the refrigerant pipe 12. A check valve 25 is provided in a middle portion of the refrigerant pipe 12 connected to the second discharge port 23 of the compressor 10.

The oil separator 24 separates oil mixed in the refrigerant. The oil separator 24 is connected to the inlet side of the oil cooler 15 via an oil pipe 26 and is configured such that the oil separated by the oil separator 24 is supplied to the oil cooler 15. Further, the outlet side of the oil cooler 15 is connected to the intermediate stage of the compressor 10 via the oil pipes 26.

An oil service valve 27 made of a three-way valve, and an oil adjustment electric valve 28 are provided in middle portions of the oil pipe 26.

The compressor 10 is configured such that the refrigerant sent from the showcase 3 is sucked by the first suction port 20 of the compressor 10 and is compressed into an intermediate pressure by the first compression mechanism, so as to be discharged from the first discharge port 21.

Further, the first discharge port 21 of the compressor 10 is connected to the inlet side of the intercooler 14 via the refrigerant pipe 12. The outlet side of the intercooler 14 is connected to the second suction port 22 of the compressor 10 via the refrigerant pipe 12.

Further, the compressor 10 is configured such that the refrigerant, which is compressed into the intermediate pressure and discharged from the first discharge port 21 of the compressor 10, is made to flow into the intercooler 14 via the refrigerant pipe 12, such that, since the blower fan 16 is operated, the refrigerant is cooled in the intercooler 14 by heat exchange with outside air blown by the blower fan 16 and is then returned to the second suction port 22 of the compressor 10, and such that, by the second compression mechanism in the compressor 10, the refrigerant is compressed to the required pressure, and is then discharged from the second discharge port 23, to be sent to the gas cooler 13 via the oil separator 24.

Further, since the blower fan 16 is operated, the refrigerant, which is sent from the compressor 10, is cooled in the gas cooler 13 by heat exchange with outside air blown by the blower fan 16. However, the carbon dioxide refrigerant is not condensed, and hence is set, as gas in the supercritical state and in the high-pressure, to the intermediate cooler 30.

Further, the gas cooler 13 is connected to the intermediate cooler 30 via the refrigerant pipe 12, and a decompression electric valve 31, which reduces the pressure of the refrigerant sent from the gas cooler 13, is provided in the middle portion of the refrigerant pipe 12 between the gas cooler 13 and the intermediate cooler 30.

A split heat exchanger 32 is connected to the refrigerant pipe 12 connected at the outlet side of the intermediate cooler 30.

A branch pipe 33 is branches from the refrigerant pipe 12 connected at the outlet side of the split heat exchanger 32, and the branch pipe 33 is connected to the split heat exchanger 32 via a liquid return expansion valve 34. The refrigerant pipe 12 and the branch pipe 33 are arranged so that the flow direction of the refrigerant in the refrigerant pipe 12 is opposite to the flow direction of the refrigerant in the branch pipe 33. The split heat exchanger 32 is configured such that the refrigerant flowing through the refrigerant pipe 12 and the refrigerant flowing through the branch pipe 33 can be efficiently heat-exchanged with each other.

A refrigerant return pipe 36 is connected to the intermediate cooler 30 via a gas return electric valve 35, and the refrigerant return pipe 36 is connected to the branch pipe 33.

An outlet service valve 37, which sends the refrigerant to each of evaporators 40 of the showcases 3, is connected to the refrigerant pipe 12 at the outlet side of the split heat exchanger 32. On the other hand, an inlet service valve 38, which returns the refrigerant from the evaporator 40 of the showcase 3, is connected to the refrigerant pipe 12 connected to the first suction port 20 of the compressor 10.

The branch pipe 33 at the outlet side of the split heat exchanger 32 is connected to the outlet side of the intercooler 14.

Further, the liquid return expansion valve 34 is configured to expand the high pressure refrigerant of the outlet side of the split heat exchanger 32 to reduce the pressure of the refrigerant to the intermediate pressure level, so that, in the split heat exchanger 32, the high pressure refrigerant flowing through the refrigerant pipe 12 is cooled by heat exchange with the decompressed refrigerant flowing through the branch pipe 33.

The refrigerant heat exchanged in the split heat exchanger 32 is mixed with the refrigerant of the outlet side of the intercooler 14 to be sent to the compressor 10 through the second suction port 22, so that the temperature of the refrigerant discharged from the compressor 10 is optimized.

Further, the evaporator 40 of each of the plurality of showcases 3 is connected to the outlet service valve 37 via a main diaphragm means 41. By the evaporator 40, the air in the refrigerator of each of the showcases 3 is cooled by being heat-exchanged with the refrigerant sent from the refrigerant pipe 12. The outlet side of the evaporator 40 is connected to the inlet service valve 38.

Further, a high-pressure sensor 50, which detects the pressure of refrigerant discharged from the compressor 10, is provided at the discharge side of the compressor 10. Also, a low-pressure sensor 51, which detects the pressure of refrigerant sucked into the compressor 10, is provided at the suction side of the compressor 10. Further, an intermediate pressure sensor 52, which detects the intermediate pressure of the refrigerant, is provided between the outlet side of the intercooler 14 and the second suction port 22 of the compressor 10.

Further, in the present embodiment, a refrigerator outlet pressure sensor 53, which detects the pressure of refrigerant sent to the showcase 3 from the refrigerator 2, is provided between the intermediate cooler 30 and the gas return electric valves 35.

Further, a refrigerator inlet temperature sensor 54, which detects the temperature of refrigerant sent from the showcase 3, is provided at the inlet side of the refrigerant pipe 12. A refrigerator outlet temperature sensor 55, which detects the temperature of refrigerant sent to the showcase 3, is provided at the outlet side of the refrigerant pipe 12.

A discharge temperature sensor 56, which detects the discharge temperature of refrigerant, is provided at the discharge side of the compressor 10. A gas cooler outlet temperature sensor 57, which detects the refrigerant temperature at the outlet of the gas cooler 13, is provided at the outlet side of the gas cooler 13.

An outside air temperature sensor 58, which detects outside air temperature, is provided in the vicinity of the gas cooler 13. A split outlet temperature sensor 59, which detects the refrigerant temperature at the outlet of the split heat exchanger 32, is provided at the outlet side of the split heat exchanger 32.

Next, a control configuration of the present embodiment will be described.

FIG. 2 is a block diagram showing the control configuration in the present embodiment.

As shown in FIG. 2, in the present embodiment, the refrigerator 2 is provided with a control apparatus 60 which integrally controls respective portions of the refrigerator 2.

The control apparatus 60 is configured to receive detection values from the high-pressure sensor 50, the low-pressure sensor 51, the intermediate pressure sensor 52, and the refrigerator outlet pressure sensor 53. Further, the control apparatus 60 is configured to receive detection values from the refrigerant discharge temperature sensor 56, the outside air temperature sensor 58, the gas cooler outlet temperature sensor 57, the refrigerator outlet temperature sensor 55, the refrigerator inlet temperature sensor 54, and the split outlet temperature sensor 59.

The control apparatus 60 is configured such that, on the basis of detection values from the respective sensors 50 to 59, and on the basis of operation setting conditions, the control apparatus 60 respectively controls the driving frequency of the compressor 10, the number of rotation of the outdoor fan, and the opening degrees of the decompression electric valve 31, the liquid return electric valve, and the gas return electric valve 35.

Further, in the present embodiment, the control apparatus 60 takes in the detection value of the refrigerator outlet pressure of the refrigerant, which pressure is detected by the refrigerator outlet pressure sensor 53. Then, the control apparatus 60 determines whether or not the refrigerator outlet pressure is lower than a predetermined value. Generally, the critical pressure of carbon dioxide refrigerant is 7.3 MPa. For this reason, when the refrigerator outlet pressure is higher than 7.3 MPa, the refrigerant cannot be liquefied in the intermediate cooler 30, and hence, the cooling performance is reduced.

Therefore, in the present embodiment, the control apparatus 60 determines whether or not the refrigerator outlet pressure of the refrigerant, which pressure is detected by the refrigerator outlet pressure sensor 53, is less than a predetermined value, for example, 7.2 MPa, which is less than 7.3 MPa. It should be noted that the predetermined value is not limited to 7.2 MPa, and can be set to any other arbitrary value.

Then, when the control apparatus 60 determines that the refrigerator outlet pressure is not less than 7.2 MPa, the control apparatus 60 further determines whether or not the high pressure of the refrigerant at the discharge side of the compressor 10 is less than a predetermined value.

The design pressure of the discharged refrigerant of the compressor 10 is set to 12 MPa. Therefore, with some margin, the control apparatus 60 further determines whether or not the high pressure of the discharged refrigerant of the compressor 10 is less than, for example, 11 MPa. When the high pressure of the discharged refrigerant is less than 11 MPa, the control apparatus 60 performs control to reduce the number of rotation of the decompression electric valve 31. It should be noted that the predetermined value is not limited to 11 MPa, and can be set to any other arbitrary value.

On the other hand, when the high pressure of the discharged refrigerant is not less than 11 MPa, the control apparatus 60 performs control to reduce the number of rotation of the compressor 10.

With such control, when the high pressure of the discharged refrigerant of compressor 10 is not less than 11 MPa, the control apparatus 60 performs control to adjust the opening degree of the decompression electric valve 31 to prevent the refrigerator outlet pressure from exceeding the critical pressure. Thereby, the control apparatus 60 can prevents that the capability of the compressor 10 is reduced more than necessary. Therefore, the cooling performance of the refrigerator 2 can be maintained.

Further, when the control apparatus 60 controls the decompression electric valve 31 or the compressor 10, the control apparatus 60 receives the detection value of the refrigerator outlet pressure of the refrigerant from the refrigerator outlet pressure sensor 53 and determines whether or not the refrigerator outlet pressure is less than a predetermined value. The predetermined value in this case is set to, for example, 6.8 MPa which is less than 7.2 MPa.

When the refrigerator outlet pressure is more than 6.8 MPa, the control apparatus 60 again determines whether or not the refrigerator outlet pressure is less than 7.2 MPa, and also determines whether or not the high pressure of the discharged refrigerant of compressor 10 is less than 11 MPa.

On the basis of the determination results, as described above, the control apparatus 60 controls the opening degree of the decompression electric valve 31 or the number of rotation of the compressor 10.

Next, the operation of the present embodiment will be described.

First, when the compressor 10 is operated, the refrigerant sent from the showcase 3 is sucked into the first suction port 20 of the compressor 10. The refrigerant is compressed into intermediate pressure by the first compression mechanism and discharged from the first discharge port 21.

Further, the refrigerant discharged from the first discharge port 21 of the compressor 10 is made to flow into the intercooler 14 via the refrigerant pipe 12. In the intercooler 14, the refrigerant is cooled by heat exchange with outside air blown by the blower fan 16 and is then returned to the second suction port 22 of the compressor 10.

The refrigerant returned from the intercooler 14 is compressed to required pressure by the second compression mechanism of the compressor 10 and is discharged from the second discharge port 23 to be sent to the gas cooler 13 via the oil separator 24.

The refrigerant sent from the compressor 10 is cooled by heat exchange with outside air blown by the blower fan 16 in the gas cooler 13 and is sent to the intermediate cooler 30.

In the split heat exchanger 32, the refrigerant cooled in the intermediate cooler 30 is further cooled by heat exchange with the refrigerant which is branched from the refrigerant pipe 12 and which is decompressed through the liquid return expansion valve 34. The refrigerant cooled in the split heat exchanger 32 in this way is set to the showcase 3 via the outlet service valve 37.

Further, the refrigerant sent to the showcase 3 is decompressed to a predetermined pressure by the main diaphragm means 41 and is subjected to heat exchange in the evaporator 40, so that the interior of the refrigerator is cooled to a predetermined temperature.

The refrigerant is made to flow out from the evaporator 40 and is returned to the compressor 10 via the inlet service valve 38 and the refrigerant pipe 12.

Next, the control operation of the present embodiment will be described with reference the flowchart shown in FIG. 3.

FIG. 3 is a flowchart showing the control operation of the present embodiment.

As shown in FIG. 3, when the operation is started, the control apparatus 60 receives the value of the refrigerator outlet pressure of the refrigerant, which value is detected by the refrigerator outlet pressure sensor 53, and determines whether or not the refrigerator outlet pressure is less than 7.2 MPa (ST1). When determining that the refrigerator outlet pressure is less than 7.2 MPa (ST1: YES), the control apparatus 60 performs ordinary control (ST2).

When determining that the refrigerator outlet pressure is not less than 7.2 MPa (ST1: NO), the control apparatus 60 determines whether or not the high pressure of the discharged refrigerant of the compressor 10 is less than 11 MPa (ST3). Then, when the high pressure of the discharged refrigerant is less than 11 MPa (ST3: YES), the control apparatus 60 performs control to reduce the opening degree of the decompression electric valve 31 (ST4).

On the other hand, when the high pressure is not less than 11 MPa (ST3: NO), the control apparatus 60 performs control to reduce the number of rotation of the compressor 10 (ST5).

Then, after the control of the decompression electric valve 31 or the compressor 10, the control apparatus 60 receives the value of the refrigerator outlet pressure of the refrigerant, which value is detected by the refrigerator outlet pressure sensor 53, and determines whether or not the refrigerator outlet pressure is less than 6.8 MPa (ST6).

When determining that the refrigerator outlet pressure is less than 6.8 MPa (ST6: YES), the control apparatus 60 performs ordinary control (ST2).

On the other hand, when determining that the refrigerator outlet pressure is not less than 6.8 MPa (ST6: NO), the control apparatus 60 maintains the opening degree of the decompression electric valve 31 and the number of rotation of the compressor 10 during a period of time (ST7). Then, the control apparatus 60 again determines whether or not the refrigerator outlet pressure, detected by the refrigerator outlet pressure sensor 53, is less than 7.2 MPa (ST1).

On the basis of the determination result, as described above, the control apparatus 60 controls the opening degree of the decompression electric valve 31 or the number of rotation of the compressor 10. The control apparatus 60 repeats this operation until the refrigerator outlet pressure becomes less than the critical pressure.

As described above, in the present embodiment, when the outlet pressure of the refrigerator 2 becomes higher than the critical pressure, the control apparatus 60 performs control to reduce the opening degree of the decompression electric valve 31 provided at the upstream side of the intermediate cooler 30.

As a result, in the intermediate cooler 30, gas-liquid separation is performed and thereby the refrigerant is liquefied, as a result of which the refrigerator outlet pressure can be lower than the critical pressure, and the liquid refrigerant can be sent to the showcase 3. Thereby, at the inlet side of the main diaphragm means 41 of the showcase 3, the specific enthalpy of the refrigerant is reduced so that the cooling effect is increased.

FIG. 4 is a p-h diagram in the control of the present invention, and a p-h diagram in the conventional control.

As shown in FIG. 4, in the conventional control, when the refrigerator outlet pressure is higher than 7.3 MPa, the gas-liquid separation is not performed, and the specific enthalpy cannot be reduced.

On the contrary, in the control in the present invention, the refrigerator outlet pressure can be lower than 7.3 MPa, and hence, the gas-liquid separation can be performed in the intermediate cooler 30 so that the refrigerant is liquefied. As a result, the specific enthalpy of the refrigerant at the inlet side of the main diaphragm means 41 can be reduced, and thereby, the cooling effect can be increased.

Further, in the present embodiment, when the difference between the high pressure at the discharge side of the compressor 10 and the design pressure is less than 1 MPa, the control apparatus 60 performs control to reduce the amount of rotation of the compressor 10.

Thereby, the amount of rotation of the compressor 10 can be reduced, and thereby, the outlet pressure of the refrigerator can be reduced.

In this case, when the amount of rotation of the compressor 10 is reduced, the circulation amount of refrigerant is reduced. However, since the specific enthalpy of the refrigerant can also be reduced, the cooling effect can be increased, and the cooling capacity can be increased.

According to the present embodiment, when the difference between the high pressure at the discharge side of the compressor 10 and the design pressure is less than 1 MPa, the control apparatus 60 performs control to secure the difference between the high pressure at the discharge side of the compressor 10 and the design pressure by reducing the amount of rotation of the compressor 10, and then performs control to reduce the opening degree of the decompression electric valve 31.

Thereby, after the difference between the high pressure at the discharge side of the compressor 10 and the design pressure is secured, the opening degree of the decompression electric valve 31 can be reduced, and thereby, the refrigerator outlet pressure can be reduced.

It should be noted that the present invention is not limited to the above-described embodiment, and various modifications and variations are possible within the scope and spirit of the present invention.

DESCRIPTION OF SYMBOLS

-   1 Refrigeration apparatus -   2 Refrigerator -   3 Showcase -   10 Compressor -   11 Refrigeration heat exchanger -   13 Gas cooler -   14 Intercooler -   15 Oil cooler -   16 Blower fan -   26 Oil pipes -   28 Oil adjustment electric valve -   30 Intermediate cooler -   31 Decompression electric valve -   32 Split heat exchanger -   33 Branch pipe -   34 Liquid return expansion valve -   35 Gas return electric valve -   40 Evaporator -   41 Main diaphragm means -   50 High-pressure sensor -   51 Low-pressure sensor -   52 Intermediate pressure sensor -   53 Refrigerator outlet pressure sensor -   54 Refrigerator inlet temperature sensor -   55 Refrigerator outlet temperature sensor -   56 Discharge temperature sensor -   57 Gas cooler outlet temperature sensor -   58 Outside air temperature sensor -   59 Split outlet temperature sensor -   60 Control apparatus 

What is claimed is:
 1. A refrigeration apparatus including: a refrigerator having a two-stage compression compressor, an intercooler, a gas cooler, a decompression electric valve, an intermediate cooler, and a gas return electric valve; and a showcase having main diaphragm means and a evaporator, the refrigeration apparatus comprising a control apparatus which performs control to reduce the opening degree of the decompression electric valve at the upstream side of the intermediate cooler, when the outlet pressure of the refrigerator is higher than critical pressure.
 2. The refrigeration apparatus according to claim 1, wherein, when the difference between the high pressure at the discharge side of the compressor and a design pressure is less than 1 MPa, the control apparatus performs control to reduce the amount of rotation of the compressor.
 3. The refrigeration apparatus according to claim 2, wherein, when the difference between the high pressure at the discharge side of the compressor and the design pressure is less than 1 MPa, the control apparatus performs control to reduce the amount of rotation of the compressor, and after securing the difference between the high pressure at the discharge side of the compressor and the design pressure, the control apparatus performs control to reduce the opening degree of the decompression electric valve. 